page_title: Therapsid
section_title: Evolutionary history
hierarchical_section_title: Therapsid / Evolutionary history
caption_attribution_description: English: Sketch of Raranimus dashankouensis - probably most primitive therapsid. Русский: Набросок головы Raranimus dashankouensis - вероятно, самого примитивного терапсида.
context_page_description: Therapsida is a group of eupelycosaurian synapsids that includes mammals and their ancestors. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, as opposed to the sprawling posture of many reptiles and salamanders. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian.
  Therapsids evolved from "pelycosaurs", specifically within the Sphenacodontia, more than 275 million years ago. They replaced the "pelycosaurs" as the dominant large land animals in the Middle Permian and were largely replaced, in turn, by the archosauromorphs in the Triassic, although one group of therapsids, the kannemeyeriiforms, remained diverse in the Late Triassic.
  The therapsids included the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago. Of the non-mammalian therapsids, only cynodonts survived the Triassic–Jurassic extinction event. The last of the non-mammalian therapsids, the tritylodontid cynodonts, became extinct in the Early Cretaceous, approximately 100 million years ago.
context_section_description: Therapsids evolved from a group of pelycosaurs called sphenacodonts. Therapsids became the dominant land animals in the Middle Permian, displacing the pelycosaurs. Therapsida consists of four major clades: the dinocephalians, the herbivorous anomodonts, the carnivorous biarmosuchians, and the mostly carnivorous theriodonts. After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian (Guadalupian) but the anomodont dicynodonts as well as the theriodont gorgonopsians and therocephalians flourished, being joined at the very end of the Permian by the first of the cynodonts.
  Like all land animals, the therapsids were seriously affected by the Permian–Triassic extinction event; the very successful gorgonopsians dying out altogether and the remaining groups - dicynodonts, therocephalians, and cynodonts - reduced to a handful of species each by the earliest Triassic. The dicynodonts, now represented by a single family of large stocky herbivores, the Kannemeyeridae, and the medium-sized cynodonts (including both carnivorous and herbivorous forms), flourished worldwide throughout the Early and Middle Triassic. They disappear from the fossil record across much of Pangea at the end of the Carnian (Late Triassic), although they continued for some time longer in the wet equatorial band and the south.
  Some exceptions were the still further derived eucynodonts. At least three groups of them survived. They all appeared in the Late Triassic period. The extremely mammal-like family, Tritylodontidae, survived into the Early Cretaceous. Another extremely mammal-like family, Tritheledontidae, are unknown later than the Early Jurassic. Mammaliaformes was the third group, including Morganucodon and similar animals. Many taxonomists refer to these animals as "mammals", though some limit the term to the mammalian crown group.
  The non-eucynodont cynodonts survived the Permian-Triassic extinction; Thrinaxodon, Galesaurus and Platycraniellus are known from the Early Triassic. By the Middle Triassic, however, only the eucynodonts remained.
  The therocephalians, relatives of the cynodonts, managed to survive the Permian-Triassic extinction and continued to diversify through the Early Triassic period. Approaching the end of the period, however, the therocephalians were in decline to eventual extinction, likely outcompeted by the rapidly diversifying Saurian lineage of diapsids, equipped with sophisticated respiratory systems better suited to the very hot, dry and oxygen-poor world of the End-Triassic.
  Dicynodonts were long thought to have become extinct near the end of the Triassic, but there is evidence that they survived into the Cretaceous. Their fossils have been found in Gondwana. This is an example of Lazarus taxon. Other animals that were common in the Triassic also took refuge here, such as the temnospondyls.
  Mammals are the only living therapsids. The mammalian crown group, which evolved in the Early Jurassic period, radiated from a group of mammaliaforms that included the docodonts. The mammaliaforms themselves evolved from probainognathians, a lineage of the eucynodont suborder.
caption: Raranimus, a primitive therapsid
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